1. Field of the Invention
The present invention relates generally to plastic containers, and more particularly to hot-fillable containers.
2. Related Art
The use of blow molded plastic containers for packaging liquid product in “hot fill” applications is known. The term “hot fill” can be considered any temperature higher than room temperature. However, when referring to “hot fill” applications, conventional temperatures used in such applications are at least 180° F.
In the process of filling a plastic container with hot fill product, pressure or vacuum imposed on the container can result in permanent deformation of the container. The sidewalls of the container can deform as the container is being filled with hot fluids. In addition, the rigidity of the container decreases after the hot fill liquid is introduced into the container. The temperatures employed in these operations may be above the transition temperature (Tg) of the plastic used (for example PET), which can result in the deformation becoming permanent. In addition, as the liquid cools in a sealed container, gas that is also in the container shrinks in volume, producing a pressure less than atmospheric (or a “vacuum”) in the container.
Hot fill containers often have substantially rectangular vacuum panels that are designed to collapse inwardly as the contents of the container cool after the hot-fill process. These vacuum panels help reduce unwanted deformation of the container by flexing inward under the pressure of the vacuum. By flexing inward, the vacuum panels relieve the pressure created by the vacuum and prevent or reduce the deformation of other parts of the container.
U.S. Pat. No. 5,341,946 discloses vacuum panels having multiple outwardly projecting portions which are separated by a portion of the vacuum panel. U.S. Pat. Nos. 5,279,433 and 6,016,932 disclose other configurations of vacuum panels having projecting center portions. Yet another configuration of vacuum panels having projecting center portions is disclosed in WO 97/34808.
A particularly persistent problem in the manufacture of plastic containers is known in the industry as “lightweighting.” Typically, lightweighting involves redesigning a package to use less plastic material, which also tends to make the container weigh less. Manufacturers continue to develop new technologies that enable them to reduce the amount of PET resin needed to make a bottle without compromising performance. These efforts are extremely important to reduce manufacturing costs because PET resin accounts for a significant portion of the cost of the finished container. However, lightweighting of a container can result in thinner container walls. As a result, such lightweighted containers are more subject to deformation. Thus, there is a continuing need for containers that are lightweighted but still resist deformation.